Light emitting device

ABSTRACT

A light emitting device includes a substrate and a plurality of light emitting cells disposed on the substrate. Each light emitting cell includes a first semiconductor layer and a second semiconductor layer, an active layer between the first and the second semiconductors, a conductive material on the second semiconductor layer, an inclined surface, a first insulation layer overlaps each light emitting cell, an electrically conductive material overlaps the first insulation layer to couple two of the plurality of light emitting cells, and a second insulation layer overlaps the electrically conductive material. A light-transmitting material is used in both the first insulation layer and the second insulation layer. The inclined surface is continuous and has a slope of approximately 20° to approximately 80° from a horizontal plane based on the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/550,815, filed on Nov. 21, 2014, which is a continuation of U.S.patent application Ser. No. 14/015,411, filed on Aug. 30, 2013, nowissued as U.S. Pat. No. 8,895,957, which is a continuation of U.S.patent application Ser. No. 13/862,052, filed on Apr. 12, 2013, nowissued as U.S. Pat. No. 8,704,246, which is a continuation of U.S.application Ser. No. 11/993,965, filed on Dec. 26, 2007, now issued asU.S. Pat. No. 8,476,648, which is the National Stage Entry ofInternational Application No. PCT/KR2006/002427, filed on Jun. 22, 2006,and claims priority from and the benefit of Korean Patent ApplicationNo. 10-2005-0053797, filed on Jun. 22, 2005, Korean Patent ApplicationNo. 10-2005-0055179, filed on Jun. 24, 2005, and Korean PatentApplication No. 10-2006-0021801, filed on Mar. 8, 2006, all of which arehereby incorporated by reference for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION

Field of Invention

The present invention relates to a light emitting device and a method ofmanufacturing the same. More particularly, the present invention relatesto a nitride based semiconductor light emitting device with enhancedluminous efficiency and brightness and a method of manufacturing thelight emitting device.

Description of the Related Art

A light emitting device refers to an element in which minority carriers(electrons or holes) injected using a p-n junction structure of asemiconductor are produced and certain light is emitted due torecombination of the carriers. A light emitting source is formed fromany one or combination of compound semiconductor materials such as GaAs,AlGaAs, GaN, InGaN and AlGaInP, so that a variety of colors can beimplemented. For example, a red light emitting device may be formed fromGaAsP or the like; a green light emitting device may be formed from GaP,InGaN or the like; a blue light emitting device may be formed using anInGaN/GaN double hetero structure; and a UV light emitting device may beformed using an AlGaN/GaN or AlGaN/AlGaN structure.

In particular, GaN has a direct bandgap of 3.4 eV at a normaltemperature and a direct energy bandgap of 1.9 eV (InN) to 3.4 eV (GaN)or 6.2 eV (AlN) by combining with a substance such as InN or AlN. Thus,GaN is a substance with great applicability to an optical element due toits broad wavelength range from visible light to ultraviolet light.Since the wavelength can be adjusted in such a manner, full-colorimplementation can be made by means of red, green and blue lightemitting devices with a short wavelength range, so that theapplicability to a general illumination market as well as a displaydevice market is expected to be greatly increased.

Light emitting devices have characteristics of lower power consumption,longer lifespan, better installation in a narrow space and strongerresistance against vibration as compared with existing bulbs orfluorescent lamps. Since the light emitting devices are used as displaydevices and backlights and have superior characteristics in view of thereduction in power consumption and the durability, many studies forapplying the light emitting devices to a general illumination field havebeen recently conducted. In the future, their applicability is expectedto extend to a backlight of a large-sized LCD-TV, a vehicle headlightand general illumination. To this end, it is necessary to improveluminous efficiency of light emitting devices, solve a heat dissipationproblem, and achieve high brightness and output of the light emittingdevices.

Many techniques for enhancing the performance of light emitting deviceshave been currently developed. There are various indexes indicating theperformance of light emitting devices, such as luminous efficiency(lm/W), internal quantum efficiency (%), external quantum efficiency (%)and extraction efficiency (%). The extraction efficiency is determinedas a ratio of electrons injected into the light emitting device tophotons emitted to the outside of the light emitting device. That is,the light emitting device becomes bright as the extraction efficiencybecomes high. Since the extraction efficiency of the light emittingdevice is much influenced by the shape and surface pattern of a chip,the structure of a chip and a packaging type, careful attention shouldbe paid when designing the light emitting device.

FIG. 1 is a sectional view showing a conventional light emitting devicewith a horizontal structure.

Referring to FIG. 1, the light emitting device comprises a substrate 1,an N-type semiconductor layer 2 formed on the substrate 1, an activelayer 3 formed on a portion of the N-type semiconductor layer 2 and aP-type semiconductor layer 4. That is, after the N-type semiconductorlayer 2, the active layer 3 and the P-type semiconductor layer 4 havebeen sequentially formed on the substrate 1, predetermined regions ofthe P-type semiconductor layer 4 and the active layer 3 are etched toexpose a portion of the N-type semiconductor layer 2. Then, apredetermined voltage is applied to top surfaces of the exposed N-typesemiconductor layer 2 and the P-type semiconductor layer 4.

FIG. 2 is a sectional view showing a conventional light emitting devicewith a flip chip structure.

Referring to FIG. 2, the light emitting device comprises an N-typesemiconductor layer 2, an active layer 3 and a P-type semiconductorlayer 4, which are sequentially formed on a base substrate 1. The lightemitting device further comprises a submount substrate 5 onto which thebase substrate 1 is flip-chip bonded using metal bumps 8 and 9. To thisend, the N-type semiconductor layer 2, the active layer 3 and the P-typesemiconductor layer 4 are sequentially formed on the predeterminedsubstrate 1, and portions of the P-type semiconductor layer 4 and theactive layer 3 are etched to expose the N-type semiconductor layer 2such that a light emitting cell can be formed. Further, the additionalsubmount substrate 5 is prepared to form first and second electrodes 6and 7 thereon, and the P-type and N-type metal bumps 8 and 9 are thenformed on the first and second electrodes 6 and 7, respectively.Thereafter, the light emitting cell is bonded with the submountsubstrate 5 such that P and N electrodes of the light emitting cell arebonded with the P-type and N-type metal bumps 8 and 9, respectively, tofabricate a light emitting device. Since such a conventional lightemitting device with a flip chip structure has high heat dissipationefficiency and hardly has shield of light, there is an advantage in thatits light efficiency is increased by 50% or more as compared with aconventional light emitting device. Further, since a gold wire fordriving a light emitting device is not necessary, many applications to avariety of small-sized packages can be considered.

Light produced from a light emitting layer of a light emitting device isemitted from all the surfaces of a chip, and light extraction efficiencyis generally determined by a critical angle of light. However, when theconventional light emitting device is etched to expose an N-typesemiconductor layer, side surfaces of the P-type semiconductor layer andthe active layer are vertically processed such that a portion of lightproduced within the light emitting device is totally reflected on theetched surface that is processed vertically from a horizontal plane.Then, a considerable amount of light to be totally reflected is notemitted to the outside but dissipated within the light emitting devicedue to the internal reflection. That is, there is a problem in thatluminous efficiency in which electric energy is converted into lightenergy and the light is then emitted to the outside of a light emittingdevice is low.

SUMMARY OF THE INVENTION

The present invention is conceived to solve the aforementioned problems.Accordingly, an object of the present invention is to provide a lightemitting device for emitting light with high luminous intensity andbrightness by enhancing characteristics of luminous efficiency, externalquantum efficiency, extraction efficiency and the like and improvingreliability.

According to an aspect of the present invention for achieving theobjects, there is provided a light emitting device, including asubstrate and a plurality of light emitting cells disposed on thesubstrate. Each light emitting cell includes a first semiconductor layerand a second semiconductor layer, an active layer between the first andthe second semiconductors, a conductive material on the secondsemiconductor layer, an inclined surface, a first insulation layeroverlaps each light emitting cell, an electrically conductive materialoverlaps the first insulation layer to couple two of the plurality oflight emitting cells, and a second insulation layer overlaps theelectrically conductive material. A light-transmitting material is usedin both the first insulation layer and the second insulation layer. Theinclined surface is continuous and has a slope of approximately 20° toapproximately 80° from a horizontal plane based on the substrate.

In a light emitting device according to the present invention, lightproduced from a side surface of a semiconductor layer, which is notperpendicular to but inclined at a predetermined slop from a horizontalplane, is not totally reflected but emitted to the outside of the lightemitting device. Therefore, more enhanced characteristics of lightextraction efficiency, external quantum efficiency, luminous efficiencyor the like can be obtained. Further, a light emitting device of thepresent invention emits light with high luminous intensity andbrightness and can be applied to a variety of products in which asuperior light characteristic is necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description ofpreferred embodiments given in conjunction with the accompanyingdrawings, in which:

FIGS. 1 and 2 are sectional views showing conventional light emittingdevices, respectively;

FIG. 3 is a conceptual sectional view illustrating a light emittingdevice with a horizontal structure according to the present invention;

FIGS. 4 and 5 are sectional views illustrating a process ofmanufacturing a light emitting device according to a first embodiment ofthe present invention;

FIGS. 6 to 9 are sectional views illustrating a process of manufacturinga light emitting device according to a second embodiment of the presentinvention;

FIGS. 10 to 13 are sectional views illustrating a process ofmanufacturing a light emitting device according to a third embodiment ofthe present invention;

FIGS. 14 to 17 are sectional views illustrating a process ofmanufacturing a light emitting device according to a fourth embodimentof the present invention;

FIG. 18 is a conceptual sectional view illustrating a light emittingdevice with a flip chip structure according to the present invention;

FIGS. 19 to 23 are sectional views illustrating a process ofmanufacturing a light emitting device according to a fifth embodiment ofthe present invention;

FIGS. 24 to 28 are sectional views illustrating a process ofmanufacturing a light emitting device according to a sixth embodiment ofthe present invention;

FIG. 29 is a sectional view showing a seventh embodiment according tothe present invention; and

FIGS. 30 and 31 are conceptual sectional views illustrating a differencebetween effects of the light emitting devices according to the prior artand the present invention;

FIG. 32 is a sectional view illustrating a light emitting diode for ACoperation according to an eighth embodiment of the present invention;and

FIGS. 33 to 38 are sectional views illustrating a process ofmanufacturing a light emitting diode according to the eighth embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a light emitting device and a manufacturing method thereofaccording to the present invention will be described in detail withreference to the accompanying drawings. However, the present inventionis not limited to the embodiments set forth herein but can beimplemented in different forms. Rather, the preferred embodiments aremerely provided to allow the present invention to be completelydescribed herein and to fully convey the scope of the invention to thoseskilled in the art.

FIG. 3 is a conceptual sectional view illustrating a light emittingdevice with a horizontal structure according to the present invention.

Referring to FIG. 3, the light emitting device comprises a substrate 10,and an N-type semiconductor layer 20, an active layer 30 and a P-typesemiconductor layer 40, which are sequentially formed on the substrate10. Each of side surfaces of the P-type semiconductor layer 40, theactive layer 30 and a portion of the N-type semiconductor layer 20 has aslope of 80 to 20° from a horizontal plane such that a critical angle oflight can be changed by such surfaces and light can be easily extracted.Therefore, luminous efficiency of a light emitting device can beimproved.

FIGS. 4 and 5 are sectional views illustrating a process ofmanufacturing a light emitting device according to a first embodiment ofthe present invention.

Referring to FIG. 4, an N-type semiconductor layer 20, an active layer30 and a P-type semiconductor layer 40 are sequentially formed on asubstrate 10.

The substrate 10 refers to a general wafer used for fabricating a lightemitting device and is made of at least any one of Al₂O₃, SiC, ZnO, Si,GaAs, GaP, LiAl₂O₃, BN, AlN and GaN. In this embodiment, a crystalgrowth substrate made of sapphire is used.

A buffer layer (not shown) may be further formed on the substrate 10 toreduce lattice mismatch between the substrate 10 and the subsequentlayers upon growth of crystals. The buffer layer may contain GaN or AlNthat is a semiconductor material.

The N-type semiconductor layer 20 is a layer in which electrons areproduced and is preferably made from GaN doped with N-type impurities.However, the N-type semiconductor layer 20 is not limited thereto butmay use a material layer having a variety of semiconductor properties.The N-type semiconductor layer 20 including N-type Al_(x)Ga_(1-x)N(0≦x≦1) is formed in this embodiment. Further, the P-type semiconductorlayer 40 is a layer in which holes are produced and is preferably madefrom GaN doped with P-type impurities. However, the P-type semiconductorlayer 40 is not limited thereto but may use a material layer with avariety of semiconductor properties. The P-type semiconductor layer 40including P-type Al_(x)Ga_(1-x)N (0≦x≦1) is formed in this embodiment.Moreover, InGaN may be used as the semiconductor layer. Further, each ofthe N-type and P-type semiconductor layers 20 and 40 may be formed as amultiple layer.

The active layer 30 has a predetermined bandgap and is a region where aquantum well is formed so that electrons and holes are recombined. Theactive layer 30 may contain InGaN. The wavelength of light emittedthrough the combination of electrons and holes varies according to thekind of a material constituting the active layer 30. Therefore, it ispreferred that a semiconductor material contained in the active layer 30be controlled depending on a target wavelength.

The aforementioned material layers are formed through a variety ofdeposition and growth methods including MOCVD (Metal Organic ChemicalVapor Deposition), CVD (Chemical Vapor Deposition), PCVD(Plasma-enhanced Chemical Vapor Deposition), MBE (Molecular BeamEpitaxy), HVPE (Hybride Vapor Phase Epitaxy) and the like.

Thereafter, portions of the P-type semiconductor layer 40 and the activelayer 30 are removed through a predetermined etching process to expose aportion of the N-type semiconductor layer 20. An etching mask pattern isformed on the P-type semiconductor layer 40, and the P-typesemiconductor layer 40 and the active layer 30 are then removed througha dry or wet etching process to expose the N-type semiconductor layer20.

Generally, in order to perform the etching process, a photoresist hasbeen applied onto a top surface of the P-type semiconductor layer 40 ata thickness of 1 to 2 μm, and then soft-baked at a temperature of 80 to90° C. is performed. Next, an exposure process in which light in a UVrange is irradiated through a predetermined photo mask to transfer apattern formed on the mask to the applied photoresist is executed.Thereafter, the photoresist is hard-baked at a temperature of 100 to120° C., and a developing process in which the photoresist at a portionwith relatively weak combination through the exposure process is meltedusing a solvent is executed. A predetermined etching mask pattern isformed on the P-type semiconductor layer 40 through the above process.

However, in this embodiment, the photoresist is applied at a thicknessof 3 to 50 μm which is thicker as compared with the prior art when theetching mask pattern is formed, and the exposure process is performedafter the soft-baking Next, if the photoresist is directly developedwithout the hard-baking, a developed side surface of the remainingphotoresist is formed into an inclined surface not perpendicular (90°)to but inclined at a predetermined slope from a horizontal plane.Subsequently, if exposed regions of the P-type semiconductor layer 40,the active layer 30 and the predetermined N-type semiconductor layer 20are etched using the etching mask pattern with such a slope of the sidesurface, the side surfaces of the etched P-type semiconductor layer 40,active layer 30 and N-type semiconductor layer 20 can be similarlyformed into an inclined surface not perpendicular (90°) to but inclinedat a predetermined slope from the horizontal plane.

That is, after the photoresist has been applied at a thickness of 3 to50 μm on the P-type semiconductor layer 40 of FIG. 4 and light-exposed,a developed etching mask pattern is immediately formed without thehard-baking. The P-type semiconductor layer 40 and the active layer 30,which are exposed through the etching mask pattern, are removed throughan ICP (Inductive Coupled Plasma) or dry etching process to expose theN-type semiconductor layer 20. A portion of the exposed N-typesemiconductor layer 20 may be further removed. Thereafter, if theetching mask pattern is removed, a light emitting device in which theside surfaces of the P-type semiconductor layer 40, the active layer 30and a portion of the N-type semiconductor layer 20 are not perpendicular(90°) to but inclined at the predetermined slope from a horizontal planecan be manufactured as shown in FIG. 5.

Alternatively, after a photoresist has been applied at a thickness of 3to 50 μm on the P-type semiconductor layer 40 of FIG. 4 andlight-exposed, hard-baking may be performed. In such a case, if thephotoresist is hard-baked at a temperature of 100 to 140° C. and thendeveloped, the side surface of the developed photoresist may be etchedto have a slope of 80 to 20° from a horizontal plane. For example, in acase where the hard-baking is performed at a temperature of 100° C., anetching mask pattern with a slope of about 80° from the horizontal planecan be obtained, and the side surfaces of the P-type semiconductor layer40, the active layer 30 and a portion of the N-type semiconductor layer20 can have a slope of about 80° from the horizontal plane using theetching mask pattern. Further, in a case where the hard-baking isperformed at a temperature of 140° C., an etching mask pattern with aslope of about 20° from the horizontal plane can be obtained, and theside surfaces of the P-type semiconductor layer 40, the active layer 30and a portion of the N-type semiconductor layer 20 can have a slope ofabout 20° from the horizontal plane using the etching mask pattern.

The etching mask pattern, which the photoresist with a thickness of 3 to50 μm has been light-exposed and hard-baked at a temperature of 100 to140° C. and then developed in such a manner, can be used such that theside surfaces of the etched the P-type semiconductor layer 40, activelayer 30 and predetermined N-type semiconductor layer 20 have a slope of80 to 20° from a horizontal plane similarly to the etching mask pattern.Then, light produced within a light emitting layer is not totallyreflected on the etched side surface with a variety of slopes butemitted to the outside of a light emitting device.

A transparent electrode layer may be further formed on the P-typesemiconductor layer 40 to reduce resistance of the P-type semiconductorlayer 40 and enhancing transmittance of light, and an additional ohmicmetal layer may be further formed on the P-type semiconductor layer 40or the exposed N-type semiconductor layer 20 to facilitate currentsupply. The transparent electrode layer may be made of ITO (Indium TinOxide), ZnO or a transparent conductive metal, and the ohmic metal layermay be made of Cr or Au. Further, for the application of voltage, aP-type electrode may be further formed on the P-type semiconductor layer40 and an N-type electrode may be further formed on the N-typesemiconductor layer 20.

Further, in order to enhance the heat dissipation characteristic of alight emitting device, after a rear surface of the substrate 10 has beenremoved at a predetermined thickness, Al, Ti, Ag, W, Ni, Ta, Ru or analloy thereof may be deposited on the rear surface of the substrate 10.

As can be seen from this figure, a plurality of light emitting devicesmay be fabricated on a single substrate 10, which is cut into theindividual light emitting devices. At this time, portions A shown inFIG. 5 are cutting portions used for individually cutting the pluralityof light emitting devices.

Accordingly, a light emitting device in which the side surfaces of theP-type semiconductor layer 40, the active layer 30 and a portion of theN-type semiconductor layer 20 is not perpendicular (90°) to but inclinedat the predetermined slope from a horizontal plane can be manufactured.

The aforementioned process of manufacturing a light emitting deviceaccording to the present invention is merely a specific embodiment, butis not limited thereto. Various processes and manufacturing methods maybe modified or added depending on the characteristics of devices and theconvenience of processes.

FIGS. 6 to 7 are sectional views illustrating a process of manufacturinga light emitting device according to a second embodiment of the presentinvention.

The second embodiment of the present invention is almost the same as thefirst embodiment. In the second embodiment, however, there is provided alight emitting device in which a plurality of light emitting cells areconnected in series, parallel or series-parallel in a wafer level toreduce the size of the device, and they can be driven at proper voltageand current to be used for illustration purpose and can also be driveneven with an AC power source. Descriptions overlapping with the previousembodiment will be omitted herein.

Referring to FIG. 6, an N-type semiconductor layer 20, an active layer30 and a P-type semiconductor layer 40 are sequentially formed on asubstrate 10 through various deposition methods including MOCVD (MetalOrganic Chemical Vapor Deposition), CVD (Chemical Vapor Deposition),PCVD (Plasma-enhanced Chemical Vapor Deposition), MBE (Molecular BeamEpitaxy), HVPE (Hybride Vapor Phase Epitaxy) and the like. A bufferlayer may be further formed on the substrate 10 to reduce latticemismatch between the substrate 10 and the subsequent layers upon growthof crystals.

Thereafter, portions of the P-type semiconductor layer 40 and the activelayer 30 are removed through a predetermined etching process to expose aportion of the N-type semiconductor layer 20. That is, after thephotoresist has been applied at a thickness of 3 to 50 μm on the P-typesemiconductor layer 40 of FIG. 6 and light-exposed, it is developedwithout hard-baking to form an etching mask pattern. The P-typesemiconductor layer 40 and the active layer 30, which are exposedthrough the etching mask pattern, are removed through an ICP (InductiveCoupled Plasma) or dry etching process to expose the N-typesemiconductor layer 20. A portion of the exposed N-type semiconductorlayer 20 may be further removed. Thereafter, if the etching mask patternis removed, a light emitting device in which the side surfaces of theP-type semiconductor layer 40, the active layer 30 and the N-typesemiconductor layer 20 are not perpendicular (90°) to but inclined atthe predetermined slope from a horizontal plane can be manufactured asshown in FIG. 7.

Alternatively, after a photoresist has been applied in a thickness of 3to 50 μm on the P-type semiconductor layer 40 of FIG. 6 andlight-exposed, it is hard-baked at a temperature of 100 to 140° anddeveloped such that an etching mask pattern can be formed. After theP-type semiconductor layer 40 and the active layer 30, which are exposedthrough the etching mask pattern, have been etched, the etching maskpattern is removed such that the side surfaces of the etched P-typesemiconductor layer 40 and active layer 30 can have a variety of slopesof 80 to 20°.

Next, in order to form a plurality of light emitting cells on thesubstrate 10, predetermined regions of the exposed N-type semiconductorlayer 20 are removed such that a portion of the substrate 10 can beexposed. To this end, a predetermined mask pattern is formed on all theportions except the predetermined regions where the substrate 10 will beexposed, and regions of the N-type semiconductor layer 20 that areexposed through the mask pattern are then etched such that the pluralityof light emitting cells can be electrically isolated from one another asshown in FIG. 8. At this time, the mask pattern whose side surface isinclined through the aforementioned process is formed and then used toetch the exposed N-type semiconductor layer 20 such that the sidesurfaces of the P-type semiconductor layer 20 and the active layer 30are not perpendicular to but inclined at a predetermined slope from ahorizontal plane.

Referring to FIG. 9, the N-type semiconductor layer 20 of a lightemitting cell and the P-type semiconductor layer 40 of the adjacentlight emitting cell are connected through a predetermined wiringprocess. That is, the exposed N-type semiconductor layer 20 of one lightemitting cell and the P-type semiconductor layer 40 of another adjacentlight emitting cell are connected through a wire 60. At this time, theconductive wire 60 for electrically connecting the N-type and P-typesemiconductor layers 20 and 40 are formed through a bridge process.

The aforementioned bridge process is also called an air-bridge process.In the air-bridge process, a photosensitive liquid is applied betweenchips to be connected with each other through a photo process anddeveloped to form a photoresist pattern, a material such as metal isfirst formed into a thin film on the photoresist pattern through avacuum vapor deposition method or the like, and a conductive materialcontaining gold (Au) is applied at a predetermined thickness onto thethin film through an electroplating, electroless plating or metal vapordeposition method. Thereafter, if the photoresist pattern is removedwith a solution of a solvent or the like, a lower portion of theconductive material is completely removed, and thus, only thebridge-shaped conductive material is formed in a space between theadjacent light emitting cells.

The wire 60 may be made of not only metal but also all kinds ofconductive materials. It will be apparent that a silicone compound dopedwith impurities may be used.

Further, in order to apply an external voltage to the light emittingdevice, a P-type bonding pad 50 is formed on the P-type semiconductorlayer 40 of the light emitting cell positioned at one edge of thesubstrate 10 and an N-type bonding pad 55 is formed on the exposedN-type semiconductor layer 20 of the light emitting cell positioned atthe other edge of the substrate 10.

The aforementioned process of manufacturing a light emitting deviceaccording to the present invention is merely a specific embodiment butis not limited thereto. Various modifications can be made or variousmaterial films can be further added. For example, in order to enhancethe heat dissipation characteristic of a light emitting device, after arear surface of the substrate 10 has been removed at a predeterminedthickness, Al, Ti, Ag, W, Ni, Ta, Ru or an alloy thereof may bedeposited on the rear surface of the substrate 10.

Accordingly, a light emitting device in which the plurality of lightemitting cells each of which side surfaces of the P-type semiconductorlayer 40, the active layer 30 and a portion of the N-type semiconductorlayer 20 are not perpendicular (90°) to but inclined at predeterminedslope from a horizontal plane are connected with one another can bemanufactured.

FIGS. 10 to 13 are sectional views illustrating a process ofmanufacturing a light emitting device according to a third embodiment ofthe present invention.

The third embodiment is almost the same as the second embodiment. In thesecond embodiment, the N-type semiconductor layer 20 is first exposedand a portion of the exposed N-type semiconductor layer 20 is thenremoved to separate the light emitting cells from one another. In thethird embodiment, however, a plurality of light emitting cells are firstseparated, and a portion of an N-type semiconductor layer 20 is thenexposed. Descriptions overlapping with the previous embodiments will beomitted herein.

Referring to FIG. 10, portions of an N-type semiconductor layer 20, anactive layer 30 and a P-type semiconductor layer 40, which aresequentially formed on a substrate 10, are removed to form a pluralityof light emitting cells. To this end, after a photoresist has beenapplied at a thickness of 3 to 50 μm on the P-type semiconductor layer40 and light-exposed, it is immediately developed without hard-bakingsuch that an etching mask pattern can be formed. The portions of theP-type semiconductor layer 40, the active layer 30 and the N-typesemiconductor pattern 20, which are exposed through the etching maskpattern, and the etching mask pattern is removed to separate the lightemitting cells from one another. Accordingly, a light emitting device inwhich entire side surfaces of the P-type semiconductor layer 40, theactive layer 30 and the N-type semiconductor layer 20 are notperpendicular (90°) to but inclined at a predetermined slope can beobtained as shown in this figure. Further, the P-type semiconductorlayer 40, the active layer 30 and the N-type semiconductor layer 20 areremoved using the etching mask pattern in which a photoresist is appliedat a thickness of 3 to 50 μm on the P-type semiconductor layer 40 andlight-exposed and hard-baked at a temperature of 100 to 140° and thendeveloped. Accordingly, the entire side surfaces of the P-typesemiconductor layer 40, the active layer 30 and the N-type semiconductorlayer 20 can be formed at various slopes of 80 to 20°.

Thereafter, as shown in FIG. 11, portions of the P-type semiconductorlayer 40 and the active layer 30 are removed to expose a portion of theN-type semiconductor layer 20 through a predetermined etching process.

Referring to FIG. 12, the N-type semiconductor layer 20 of one lightemitting cell and the P-type semiconductor layer 40 of another adjacentlight emitting cell are connected with each other through a bridgeprocess.

Further, in order to apply an external voltage to the light emittingdevice, a P-type bonding pad 50 is formed on the P-type semiconductorlayer 40 of the light emitting cell positioned at one edge of thesubstrate 10 and an N-type bonding pad 55 is formed on the exposedN-type semiconductor layer 20 of the light emitting cell positioned atthe other edge of the substrate 10.

The aforementioned process of manufacturing a light emitting deviceaccording to the present invention is merely a specific embodiment butis not limited thereto. Various modifications can be made and variousmaterial films may be further added. For example, in order to enhancethe heat dissipation characteristic of a light emitting device, after arear surface of the substrate 10 has been removed at a predeterminedthickness, Al, Ti, Ag, W, Ni, Ta, Ru or an alloy thereof may bedeposited on the rear surface of the substrate 10.

Further, even in a case where the plurality of light emitting cells areseparated by etching such that the side surfaces may have various slopesas shown in FIG. 10 and then etched to expose the N-type semiconductorlayer 20, a light emitting device can be manufactured using the sameetching process as described above. That is, as shown in FIG. 13, theside surfaces of the P-type semiconductor layer 40 and the active layer30, which are etched to expose the N-type semiconductor layer 20, can beformed at various slopes.

Accordingly, a light emitting device in which the plurality of lightemitting cells each of which side surfaces of the P-type semiconductorlayer 40, the active layer 30 and the N-type semiconductor layer 20 arenot perpendicular (90°) to but inclined at predetermined slope from ahorizontal plane are connected with one another can be manufactured.

FIGS. 14 to 17 are sectional views illustrating a process ofmanufacturing a light emitting device according to a fourth embodimentof the present invention.

The fourth embodiment is almost the same as the third embodiment. In thethird embodiment, a conductive wire for electrically connecting theN-type semiconductor layer of one light emitting cell and the P-typesemiconductor layer of another adjacent light emitting cell is formedthrough a bridge process. In the fourth embodiment, however, theconductive wire is formed through a step coverage process. Descriptionsoverlapping with the previous embodiments will be omitted herein.

Referring to FIG. 14, even in a case where a plurality of light emittingcells are separated by etching such that the side surfaces may havevarious slopes and then etched to expose an N-type semiconductor layer20 through the aforementioned process, the side surfaces of P-typesemiconductor layer 40 and active layer 30, which are etched to exposethe N-type semiconductor layer 20, are formed with various slopes.Further, in order to reduce the resistance of the P-type semiconductorlayer 40 and enhance the transmittance of light, a transparent electrodelayer 85 may be further formed on a top surface of the P-typesemiconductor layer 40. Further, an additional ohmic metal layer 87 forfacilitating the supply of current may be further formed on a topsurface of the P-type semiconductor layer 40 or the exposed N-typesemiconductor layer 20. The transparent electrode layer 85 may be madeof ITO (Indium Tin Oxide), ZnO or a conductive transparent metal, andthe ohmic metal layer 87 may be made of Cr or Au.

Referring to FIG. 15, a continuous insulation layer 70 is formed on anentire surface of the substrate 10 with the plurality of light emittingcells formed thereon. The insulation layer 70 covers the side surfacesand top surfaces of the light emitting cells and the top surfaces of thesubstrate 10 between the adjacent light emitting cells. For example, theinsulation layer 70 may be formed as a silicone oxide film using a CVD(Chemical Vapor Deposition) technique.

Since the side surfaces of the light emitting cells are inclined, theinsulation layer 70 can easily cover the side surfaces of the lightemitting cells. Since the total thickness of the N-type semiconductorlayer 20 and active layer 30 is small and spaces between the adjacentP-type semiconductor layers 40 are broad, the side surfaces of theP-type semiconductor layers 40 adjacent to the exposed regions of theN-type semiconductor layers 20 can be easily covered with the insulationlayer 70.

Referring to FIG. 16, an opening portion is formed on each of theexposed N-type and P-type semiconductor layers 20 and 40 of the lightemitting cell by patterning the insulation layer 70 through apredetermined etching process. If the transparent electrode layer 85and/or the ohmic metal layer 87 are formed as shown in this figure, thetransparent electrode layer 85 and/or the ohmic metal layer 87 areexposed through the opening portion.

Referring to FIG. 17, a wire 80 is formed on the insulation layer 70with the opening portion. The wire 80 connects the N-type and P-typesemiconductor layers 20 and 40 through the opening portion thereof. Thatis, the N-type semiconductor layer 20 of one light emitting cell and theP-type semiconductor layer 40 of another adjacent the light emittingcell are electrically connected with the wire.

The wire 80 may be formed using a plating technique. That is, after anetching mask pattern with an opening portion defining a region of thewire 80 has been formed on the insulation layer 70 and a metal layer hasbeen plated within the opening portion, the etching mask pattern isremoved and thus the wire 80 can be formed.

Further, the wire 80 may be formed using the CVD (Chemical VaporDeposition) or PVD (Physical Vapor Deposition) technique. That is, ametal layer is formed using a vapor deposition technique such aselectron beam deposition and then patterned using a photo and etchingprocess, so that the wire 80 can be formed. Since the side surface ofthe light emitting cell is inclined, the metal layer is continuouslyformed on the upper side surface of the light emitting cell.

The light emitting device in which the wire 80 is formed as describedabove has an advantage in that it is possible to prevent the wire 80from being disconnected or shorted due to external pressure and alsoprevent conductive materials such as metal, which remains while the wire80 is formed, from shorting the light emitting cell.

Accordingly, a light emitting device in which the plurality of lightemitting cells each of which side surfaces of the P-type semiconductorlayer 40, the active layer 30 and the N-type semiconductor layer 20 arenot perpendicular (90°) to but inclined at predetermined slope from ahorizontal plane are connected with one another can be manufactured.

As described above, the light emitting device according to the presentinvention is formed such that the side surfaces of the P-typesemiconductor layer, the active layer and a portion of the N-typesemiconductor layer are not perpendicular (90°) to but inclined at apredetermined slope from a horizontal plane. Therefore, luminousefficiency of the light emitting device of the present invention can beenhanced as compared with that of the conventional light emittingdevice. The reason is that a photon reflected on a flat surface in theprior art is not reflected on a surface with a different angle butemitted to the outside.

FIG. 18 is a conceptual sectional view illustrating a light emittingdevice with a flip chip structure according to the present invention.

Referring to FIG. 18, the light emitting device comprises a lightemitting layer, i.e. an N-type semiconductor layer 120, an active layer130 and a P-type semiconductor layer 140 sequentially formed on a basesubstrate 110. Further, the light emitting device comprises a submountsubstrate 200 onto which the base substrate 110 with the light emittinglayer formed thereon is flip-chip bonded through metal bumps 150 and155. A side surface of the light emitting layer comprising the P-typesemiconductor layer 140, the active layer 130 and the N-typesemiconductor layer 120 is inclined at a slope of 20 to 80° from thehorizontal plane and a critical angle of light is changed due to theside surface such that the light can be easily extracted. Therefore,luminous efficiency of the light emitting device can be improved.

FIGS. 19 to 23 are sectional views illustrating a process ofmanufacturing a light emitting device according to a fifth embodiment ofthe present invention.

Referring to FIG. 19, an N-type semiconductor layer 120, an active layer130 and a P-type semiconductor layer 140 are sequentially formed on abase substrate 110.

The base substrate 110 refers to a general wafer used for fabricating alight emitting device is made of a transparent substrate such as Al₂O₃,ZnO and LiAl₂O₃. In this embodiment, a crystal growth substrate made ofsapphire is used.

The N-type semiconductor layer 120, the active layer 130 and the P-typesemiconductor layer 140 are sequentially formed on the substrate 110through various deposition methods including MOCVD (Metal OrganicChemical Vapor Deposition), CVD (Chemical Vapor Deposition), PCVD(Plasma-enhanced Chemical Vapor Deposition), MBE (Molecular BeamEpitaxy), HVPE (Hybride Vapor Phase Epitaxy) and the like. A bufferlayer may be further formed on the substrate 110 to reduce latticemismatch between the substrate 110 and the subsequent layers upon growthof crystals. The aforementioned components are the same as those in theprevious embodiments, and thus, descriptions overlapping with theforegoing components will be omitted herein.

Thereafter, portions of the P-type semiconductor layer 140 and theactive layer 130 are removed through a predetermined etching process toexpose a portion of the N-type semiconductor layer 120. This etchingprocess is the same as that of the previous embodiments.

That is, after a photoresist has been applied at a thickness of 3 to 50μm on the P-type semiconductor layer 140 of FIG. 19 and light-exposed,it is immediately developed without hard-baking to form an etching maskpattern. The P-type semiconductor 140 and the active layer 130, whichare exposed through the etching mask pattern, are removed through an ICP(Inductive Coupled Plasma) or dry etching process to expose the N-typesemiconductor layer 120. Thereafter, if the etching mask pattern isremoved, side surfaces of the P-type semiconductor layer 140 and theactive layer 130 which are not perpendicular (90°) to but inclined at apredetermined slope from the horizontal plane can be obtained as shownin FIG. 20.

Alternatively, after a photoresist has been applied at a thickness of 3to 50 μm on the P-type semiconductor layer 140 of FIG. 19 andlight-exposed, it is hard-baked at a temperature of 100 to 140° C. andthen developed such that an etching mask pattern can be formed. Afterthe P-type semiconductor layer 140 and the active layer 130, which areexposed through the etching mask pattern, have been etched, the etchingmask pattern is removed such that the side surfaces of the etched P-typesemiconductor layer 140 and active layer 130 can have a variety ofslopes of 80 to 20°.

A reflection layer for reflecting light may be further formed on a topsurface of the P-type semiconductor layer 140, and an additional ohmicmetal layer for facilitating the supply of current may be further formedon a top surface of the P-type semiconductor layer 140 or the exposedN-type semiconductor layer 120. The ohmic metal layer may be made of Cror Au.

Further, P-type and N-type metal bumps 155 and 150 are formed on theP-type and N-type semiconductor layers 140 and 120, respectively, asshown in FIG. 21. Each of the P-type and N-type metal bumps 155 and 150may be made of at least one material selected from the group consistingof Pb, Sn, Au, Ge, Cu, Bi, Cd, Zn, Ag, Ni, Ti and an alloy thereof. Tothis end, a photoresist is applied onto an entire structure and aphotoresist pattern (not shown) through which portions of the P-type andN-type semiconductor layers 140 and 120 are exposed is formed through aphoto-etching process using a predetermined mask. After a metal film hasbeen deposited on the entire structure, metal film portions formed onregions other than regions on the P-type and N-type semiconductor layers140 exposed through the photoresist pattern and the photoresist patternare removed. Accordingly, the P-type and N-type metal bumps 155 and 150are formed on the P-type and N-type semiconductor layers 140 and 120,respectively.

Next, referring to FIG. 22, an additional submount substrate 200 isprepared to form P-type and N-type bonding pads 215 and 210 connected tothe P-type and N-type metal bumps 155 and 150, respectively.

At this time, various kinds of superior heat conductive substrates 200are used as the submount substrate 200. That is, the submount substrate200 may be made of SiC, Si, Ge, SiGe, AlN, metal or the like. In thisembodiment, AlN with superior heat conductivity and insulation propertyis used. The present invention is not limited thereto, but a metallicmaterial with superior heat and electric conductivity may be employed.In this case, an insulation or dielectric film is formed on thesubstrate 200 to sufficiently serve as an insulation. The dielectricfilm may be made of SiO2, MgO and SiN or an insulating material.Further, each of the P-type and N-type bonding pads 210 and 215 is madeof a metal with superior electric conductivity. This is formed through ascreen printing process or a deposition process using a predeterminedmask pattern.

Thereafter, the submount substrate 200 is flip-chip bonded onto the basesubstrate 110 with the light emitting layer formed thereon.

Referring to FIG. 23, in the light emitting device of the presentinvention, the N-type and P-type metal bumps 150 and 155 formed on thetop of the light emitting layer are bonded and connected with the N-typeand P-type bonding pads 210 and 215 of the submount substrate 200,respectively. At this time, the bonding pads and metal bumps may bebonded using heat or ultrasonic waves or simultaneously using the heatand ultrasonic waves. The metal bumps 150 and 155 and the lower bondingpads 210 and 215 are connected through a variety of bonding methods.

Moreover, the N-type and P-type metal bumps 150 and 155 are not formedon the top of the light emitting layer but may be formed on the submountsubstrate 200.

As can be seen from this figure, a plurality of light emitting devicesmay be fabricated on a single substrate 10, which is cut into theindividual light emitting devices. At this time, portions A shown inFIG. 23 are cutting portions used for individually cutting the pluralityof light emitting devices.

The aforementioned process of manufacturing a light emitting deviceaccording to the present invention is merely a specific embodiment, butis not limited thereto. Various processes and manufacturing methods maybe modified or added depending on the characteristics of devices and theconvenience of processes. For example, in the same process as theprevious embodiments, the base substrate with the N-type semiconductorlayer, the active layer and the P-type semiconductor layer sequentiallyformed thereon is prepared as shown in FIG. 19. Then, portions of theP-type semiconductor layer, the active layer and the N-typesemiconductor layer are first removed to expose the substrate such thatthe plurality of light emitting devices can be individually isolated. Atthis time, the side surfaces of the P-type semiconductor layer, theactive layer and the N-type semiconductor layer, which are etchedthrough the aforementioned process, may be formed not to beperpendicular (90°) to but inclined at a predetermined slope.

Accordingly, a light emitting device with a flip chip structure, inwhich the side surfaces of the P-type semiconductor layer, the activelayer and a portion of the N-type semiconductor layer are notperpendicular (90°) to but inclined at the predetermined slope from thehorizontal plane, can be manufactured.

FIGS. 24 to 28 are sectional views illustrating a process ofmanufacturing a light emitting device according to a sixth embodiment ofthe present invention.

The sixth embodiment is almost the same as the fifth embodiment. In thesixth embodiment, however, there is provided a light emitting devicewith a flip chip structure, in which a plurality of light emitting cellsare connected in series, parallel or series-parallel in a wafer level toreduce the size of the device, and they can be driven at proper voltageand current to be used for illumination purpose and can also be driveneven with an AC power source. Descriptions overlapping with the previousembodiments will be omitted herein.

Referring to FIG. 24, an N-type semiconductor layer 120, an active layer130 and a P-type semiconductor layer 140 are sequentially formed on abase substrate 110 through various deposition methods including MOCVD(Metal Organic Chemical Vapor Deposition), CVD (Chemical VaporDeposition), PCVD (Plasma-enhanced Chemical Vapor Deposition), MBE(Molecular Beam Epitaxy), HVPE (Hybride Vapor Phase Epitaxy) and thelike. A buffer layer may be further formed on the substrate 110 toreduce lattice mismatch between the substrate 110 and the subsequentlayers upon growth of crystals.

Thereafter, portions of the N-type semiconductor layer 120, the activelayer 130 and the P-type semiconductor layer 140, which are sequentiallyformed on the base substrate 110, are removed to form a plurality oflight emitting cells. To this end, after a photoresist has been appliedat a thickness of 3 to 50 μm on the P-type semiconductor layer 140 ofFIG. 24 and light-exposed, it is immediately developed withouthard-baking to form an etching mask pattern. The P-type semiconductor140, the active layer 130 and the predetermined N-type semiconductorlayer 120, which are exposed through the etching mask pattern, areremoved through an ICP (Inductive Coupled Plasma) or dry etching processto separate the light emitting cells from one another. Next, if theetching mask pattern is removed, a light emitting device in which entireside surfaces of the etched P-type semiconductor layer 140, active layer130 and N-type semiconductor layer 120 are not perpendicular (90°) tobut inclined at a predetermined slope from the horizontal plane can beobtained as shown in FIG. 25.

Alternatively, after a photoresist has been applied at a thickness of 3to 50 μm on the P-type semiconductor layer 140 of FIG. 24 andlight-exposed, it is hard-baked at a temperature of 100 to 140° C. anddeveloped such that an etching mask pattern can be formed. After theP-type semiconductor layer 140, the active layer 130 and the N-typesemiconductor layer 120, which are exposed through the etching maskpattern, have been etched, the etching mask pattern is removed such thatthe side surfaces of the etched P-type semiconductor layer 140 andactive layer 130 can be inclined at various slopes of 80 to 20°.

Next, portions of the P-type semiconductor layer 140 and the activelayer 130 are removed through a predetermined etching process to exposea portion of the N-type semiconductor layer 120, as shown in FIG. 26.The exposed N-type semiconductor layer 120 of one light emitting celland the P-type semiconductor layer 140 of another adjacent lightemitting cell are connected with each other through a predeterminedconductive wire. At this time, a bridge wire 160 is made of a conductivematerial, e.g. metal. It will be apparent that the bridge wire 160 maybe made of a silicone compound doped with impurities. The bridge wire160 is formed through a bridge process.

Further, a plurality of metal bumps are formed on the top of the lightemitting cells, and P-type and N-type metal bumps 155 and 150 arefurther formed on the P-type semiconductor layer 140 of the lightemitting cell positioned at one edge of the substrate 110 and the N-typesemiconductor layer 120 of the light emitting cell positioned the otheredge of the substrate, respectively.

Next, as shown in FIG. 27, an additional submount substrate 200 isprepared, on which a plurality of bonding layers 220, a P-type bondingpad 215 positioned at one edge of the submount substrate 200 and anN-type bonding pad 210 positioned at the other edge of the submountsubstrate are formed.

Thereafter, as can be shown in FIG. 28, the aforementioned basesubstrate 110 with the plurality of light emitting cells formed thereonis flip-chip bonded onto the submount substrate 200 to fabricate thelight emitting device. The substrates are bonded with each other throughthe metal bumps 150 and 155 formed on the top of the light emitting celland the bonding layers 220 formed on the submount substrate 200,respectively. The P-type bonding pad 215 positioned at one edge of thesubmount substrate 200 is connected to the P-type metal bump 155 of thelight emitting cell positioned at one edge of the base substrate 110,whereas the N-type bonding pad 210 positioned at the other edge of thesubmount substrate 200 is connected to the N-type metal bump 150 of thelight emitting cell positioned at the other edge of the base substrate110.

The aforementioned process of manufacturing a light emitting deviceaccording to the present invention is merely a specific embodiment, butis not limited thereto. Various processes and manufacturing methods maybe modified or added depending on the characteristics of devices and theconvenience of processes. For example, in this embodiment, theconductive wire for electrically connecting the N-type semiconductorlayer of one light emitting cell and the P-type semiconductor layer ofanother adjacent light emitting cell is formed through a bridge process,and the base substrate is then flip-chip bonded onto the submountsubstrate. However, the present invention is not limited thereto. Thatis, a conductive wire for electrically connecting the N-typesemiconductor layer of one light emitting cell and the P-typesemiconductor layer of another adjacent light emitting cells may beformed through a step coverage process which is the same as in thefourth embodiment. Further, an electrode layer may be formed on thesubmount substrate when the plurality of light emitting cells areflip-chip bonded onto the submount substrate such that the N-typesemiconductor layer of one light emitting cell and the P-typesemiconductor layer of another adjacent light emitting cell areelectrically connected through the metal bumps.

Accordingly, a light emitting device in which a plurality of flip chiplight emitting cells each having a side surface of a light emittinglayer, which is not perpendicular (90°) to but inclined at apredetermined slope from the horizontal plane, are arrayed on thesubmount substrate can be manufactured. The light emitting cells may beconnected in various ways, i.e. in series, parallel or series-parallel,depending on the desired purpose.

FIG. 29 is a sectional view showing a seventh embodiment according tothe present invention.

The seventh embodiment is almost the same as the sixth embodiment. Inthis embodiment, even in a case where a plurality of light emittingcells are separated by etching such that the side surfaces may haveslopes as shown in FIG. 25 and then etched to expose an N-typesemiconductor layer, a light emitting device can be manufactured usingthe same etching process as the previous embodiment. That is, sidesurfaces of a P-type semiconductor layer 140 and an active layer 130etched to expose an N-type semiconductor layer 120 are formed withvarious slopes, as shown in FIG. 29.

Accordingly, a light emitting device in which a plurality of flip chiplight emitting cells each having an entire side surface of a lightemitting layer, which is not perpendicular (90°) to but inclined at apredetermined slope from the horizontal plane, are arrayed on thesubmount substrate can be manufactured. The light emitting cells may beconnected in various ways, i.e. in series, parallel or series-parallel,depending on the desired purpose.

As described above, the light emitting device with a flip chip structureaccording to the present invention is formed such that some sidesurfaces of a light emitting layer are not perpendicular (90°) to butinclined at a predetermined slope from the horizontal plane. Therefore,luminous efficiency of the light emitting device of the presentinvention can be enhanced as compared with that of the conventionallight emitting device. The reason is that a photon reflected on a flatsurface in the prior art is not reflected on a surface with a differentangle but emitted to the outside.

FIGS. 30 and 31 are conceptual sectional views illustrating a differencebetween effects of the light emitting devices according to the prior artand the present invention.

The light efficiency of a light emitting device may be expressed asinternal quantum efficiency and external quantum efficiency, and theinternal quantum efficiency is determined in accordance with the designand quality of an active layer. The external quantum efficiency isdetermined in accordance with a degree where a photon produced in anactive layer is emitted to the outside of a light emitting device.Referring to FIG. 30 in which a conventional light emitting device isshown, a side surface of a semiconductor layer is formed perpendicularto a horizontal plane. In such a case, some portions of photons are notpenetrated through the side surface of the semiconductor layer butreflected thereon, and totally reflected light is not emitted to theoutside but dissipated within the light emitting device. However,referring to FIG. 31 in which a light emitting device according to thepresent invention is shown, a side surface of a semiconductor layer isnot perpendicular to but inclined at a predetermined slope from ahorizontal plane. In such a case, the inclined side surface makes acritical angle of light change to help the light to be more easilyextracted. Therefore, light generated in an active layer is not totallyreflected but emitted to the outside of the light emitting device suchthat external quantum efficiency can be markedly enhanced.

FIG. 32 is a sectional view illustrating a light emitting diode for ACoperation according to the eighth embodiment of the present invention.

Referring to FIG. 32, a plurality of light emitting cells 56 aredisposed to be spaced apart in a substrate 51. The substrate 51 may beinsulating or conducting one, and may be, for example, a sapphire or asilicon carbide (SiC) substrate.

The light emitting cells 56 respectively include a lower semiconductorlayer 55, an upper semiconductor layer 59 disposed in a region of thelower semiconductor layer, and an active layer 57 disposed between thelower semiconductor layer and the upper semiconductor layer. The upperand the lower semiconductor layers may be N-type and P-type,respectively. Alternatively the upper and the lower semiconductor layersmay be P-type and N-type, respectively.

The lower semiconductor layer 55, active layer 57 and uppersemiconductor layer 59 may include a gallium nitride-basedsemiconducting material, for example, (B, Al, In, Ga)N. Elements andstoichiometry of the active layer 57 may be determined so that a lighthaving a desired wavelength, for example, ultraviolet ray or blue light,can be emitted. The lower semiconductor layer 55 and upper semiconductorlayer 59 are formed of a material having a greater bandgap compared withthe active layer 57.

The lower semiconductor layer 55 and/or the upper semiconductor layer 59may be, as illustrated, formed of a single layer or multiple layers. Theactive layer 57 may have a single-quantum-well structure or amultiple-quantum-well structure.

A buffer layer 53 may be disposed between the light emitting cells 56and the substrate 51. The buffer layer 53 is employed to reduce alattice mismatch between the substrate 51 and the lower semiconductorlayer 55 formed thereon. The buffer layer 53 may be continuous asillustrated, but it is not limited thereto. The buffer layer 53 may bedisposed under the lower semiconductor layers 55 to be discontinuous.

Side surfaces of the light emitting cells 56 are formed to be inclinedwith respect to an upper surface of the substrate 51 and get narrowedtoward upside. The inclination of the side surfaces improves emissionefficiency of a light produced in the active layer 57, and helpsconformal deposition of other layers which will be formed on the lightemitting cells 56. In the exemplary embodiment, the inclinations of theside surfaces of the respective lower semiconductor layers 55 of thelight emitting cells 56 may be in a range of approximately 15 degrees toapproximately 80 degrees.

An insulation layer 69 covers an entire surface of the light emittingcells 56. The insulation layer 69 include opening portions on otherregions of the lower semiconductor layers 55, for example, a regionadjacent to a region on which the upper semiconductor layer 59 isformed, and include opening portions on the upper semiconductor layers59. The opening portions are space apart from each other, and therefore,the side surfaces of the light emitting cells 56 are covered with theinsulation layer 69. The insulation layer 69 may cover the substrate 51in regions between the light emitting cells 56, or the buffer layer 53.The insulation layer 69 may include a silicon oxide (SiO₂) layer.

Wires 71 are formed on the insulation layer 69. The wires 71 areelectrically connected to the lower semiconductor layers 55 and theupper semiconductor layers 59 through the opening portions. In addition,the wires 71 respectively connect the lower semiconductor layers 55 andthe upper semiconductor layers 59 of the adjacent light emitting cells56 to form a series array of the light emitting cells 56. The array maybe formed in plurality, and a plurality of arrays may be connected to bereverse parallel and connected to AC power to be driven. Further, abridge rectifier (not shown) connected to the series array of the lightemitting cells may be formed, and the light emitting cells may be drivenwith AC power by the bridge rectifier. The bridge rectifier may beformed by connecting light emitting cells having substantially the samestructure as the light emitting cells using wires 71. The wires may beformed of a conductive material, for example, a doped semiconductingmaterial such as polycrystalline silicon or a metal.

Meanwhile, electrode pads may be disposed between other regions of thelower semiconductors 55 and the insulation layer 69. The electrode pads67 are exposed by the opening portions formed in other regions of thelower semiconductor layers 55. The electrode pads 67 have ohmic contactsto the lower semiconductor layers 55. The wires 71 are in contact withthe electrode pads 67 exposed by the opening portions to be electricallyconnected to the lower semiconductor layers 55.

Transparent electrode layers 65 may be disposed between the uppersemiconductor layers 59 and the insulation layers 69. The transparentelectrode layers 65 are exposed by the opening portions formed on theupper semiconductor layers 59. The transparent electrode layers 65transmit light produced in the active layer 57, and disperse and supplycurrents to the upper semiconductor layers 59. The wires 71 are incontact with the transparent electrode layers 65 exposed by the openingportions to be electrically connected to the upper semiconductor layers59. Electrode pads (not shown) may be further formed on the transparentelectrode layers 65 and the wires 71 may be in contact with theelectrode pads.

A protecting insulation layer 73 may cover the wires 71 and theinsulation layer 69. The protecting insulation layer 73 substantiallyreduces contamination of the wires 71 from moisture and so forth, anddamage of the wires 71 from external pressure. The protecting insulationlayer 73 may be formed of a light-transmitting material, for example,silicon oxide layer.

FIGS. 33 to 38 are sectional views illustrating a process ofmanufacturing a light emitting diode according to the eighth embodimentof the present invention.

Referring to FIG. 33, a lower semiconductor layer 55, an active layer57, and an upper semiconductor layer 59 are formed on a substrate 51. Abuffer layer 53 may be formed on the substrate 51 before the lowersemiconductor layer 55 is formed.

The substrate 51 may be sapphire (Al₂O₃), silicon carbide (SiC), zincoxide (ZnO), silicon (Si), gallium arsenide (GaAs), gallium phosphate(GaP), lithium-alumina (LiAl2O3), boron nitride (BN), aluminum nitride(AlN) or gallium nitride (GaN). However, it is not limited thereto andmay be variable according to a semiconducting material which is to beformed on the substrate 51.

The buffer layer 53 is formed to reduce lattice mismatch between thesubstrate 51 and the semiconductor layer 55 which is to be formedthereon. The buffer layer 53 may include, for example, gallium nitride(GaN) or aluminum nitride (AlN). When the substrate 51 is a conductivesubstrate, the buffer layer 53 may be formed of an insulation layer or asemi-insulation layer, for example, AN or semi-insulating GaN.

The lower semiconductor layer 55, active layer 57 and uppersemiconductor layer 59 may include a gallium nitride-basedsemiconducting material, for example, (B, Al, In, Ga)N. The lower andupper semiconductor layers 55 and 59 and the active layer 57 may beformed continuously or discontinuously using, for example, metal organicchemical vapor deposition (MOCVD), molecular beam epitaxy or hydridevapor phase epitaxy (HNPE) technology.

The upper and the lower semiconductor layers may be N-type and P-type,respectively. Alternatively the upper and the lower semiconductor layersmay be P-type and N-type, respectively. In the gallium nitride-basedcompound semiconductor layer, N-type semiconductor layer may be dopedwith, for example, silicon (Si), and P-type semiconductor layer may bedoped with, for example, magnesium (Mg).

Photoresist patterns 63 defining light emitting cell regions are formedon the upper semiconductor layer 59. The photoresist patterns are formedto cover the light emitting cell regions. Reflow of the photoresistpatterns 63 is performed so that side surfaces can be inclined withrespect to an upper surface of the substrate 51. The side surfaces ofthe photoresist patterns 63 may be formed to have an inclination anglein a range of approximately 15 degrees to 80 degrees with respect to theupper surface of the substrate 51.

Referring to FIG. 34, the upper semiconductor layer 59, the active layer57 and the lower semiconductor layer 55 are sequentially etched usingthe photoresist patterns 63 as etching mask. Accordingly, the shape ofthe photoresist patterns 63 is reproduced in the semiconductor layers59, 57 and 55 and the light emitting cells with inclined side surfacesare separated. The buffer layer 53 may be exposed and the exposed bufferlayer 53 may be removed by over-etching.

Thereafter, the photoresist patterns 63 are removed, and the uppersemiconductor layer and the active layer are patterned again to exposethe etched lower semiconductor layers 55. The exposed lowersemiconductor layers may be partially etched by over-etching.Accordingly, light emitting cells 56 that are spaced apart are formed onthe substrate 51. Each of the light emitting cells 56 includes the lowersemiconductor layer 55 which is spaced apart by etching, the uppersemiconductor layer 59 disposed on an upper side of a region of thelower semiconductor layer 55, and the active layer 57 disposed betweenthe lower semiconductor layer 55 and the upper semiconductor layer 59.Other region of the lower semiconductor layer 55 is exposed. Further,most of the side surfaces of the light emitting cells 56 are formed tobe inclined with respect to an upper surface of the substrate 51.Whereas, side surfaces of the upper semiconductor layers 59 adjacent toother regions of the lower semiconductor layers 55 may be formed to beinclined as illustrated, and alternatively, may be formed vertically.

Referring to FIG. 35, a transparent electrode layer 65 may be formed onthe upper semiconductor layer 59 of the light emitting cell 56. Thetransparent electrode layer 65 includes a transparent metal such asindium tin oxide (ITO) layer or Ni/Au. Further, electrode pads 67 may beformed on other regions of the lower semiconductor layers 55. Theelectrode pads 67 have an ohmic contact with the lower semiconductorlayers 55.

The transparent electrode layer 65 may be formed on the uppersemiconductor layer 59 before the photoresist patterns are formed. Thetransparent electrode layer 65 is patterned together with the uppersemiconductor layer

Referring to FIG. 36, a continuous insulation layer 69 is formed on anentire surface of the substrate 51 with the plurality of light emittingcells 56 formed thereon. The insulation layer 69 covers the sidesurfaces and top surfaces of the light emitting cells 56, and the topsurfaces of the substrate 51 between the adjacent light emitting cells56. For example, the insulation layer 69 may be formed as a siliconeoxide film using a CVD (Chemical Vapor Deposition) technique.

Since the side surfaces of the light emitting cells 56 are inclined, theinsulation layer 69 can easily cover the side surfaces of the lightemitting cells 56. Since the total thickness of the upper semiconductorlayer 59 and active layer 57 is small and spaces between the uppersemiconductor layers 59 are broad, the side surfaces of the uppersemiconductor layers 59 adjacent to other regions of the lowersemiconductor layers 55 can be easily covered with the insulation layer69.

Referring to FIG. 37, an opening portions are formed on other regions ofthe lower semiconductor layers 55 and the upper semiconductor layers 59by patterning the insulation layer 69. If the electrode pads 67 and thetransparent electrode layers 65 are formed, the electrode pads 67 andthe transparent electrode layers 65 are exposed through the openingportions.

The opening portions may be formed using a photo and etching process,and the electrode pads 67 substantially reduce damage of the lowersemiconductor layers 55 while the insulation layer 69 is etched.

Referring to FIG. 38, wires 71 are formed on the insulation layer 69with the opening portions. The wire 71 are electrically connected to thelower semiconductor layers 55 and the upper semiconductor layers 59through the opening portions, and connect the lower semiconductor layers55 and the upper semiconductor layers 59 of the adjacent light emittingcells 56 to form arrays connected in series.

The wires 71 may be formed using a plating technique. That is, the wires71 may be formed by forming a photoresist pattern having openingportions defining wire region on the insulation layer 69, plating ametal layer in the opening portions, and removing the photoresistpattern.

Alternatively, the wires 71 may be formed using CVD (Chemical VaporDeposition) or PVD (Physical Vapor Deposition) technique. That is, ametal layer is formed using a vapor deposition technique such aselectron beam deposition and then patterned using a photo and etchingprocess, so that the wires 71 can be formed. Since the insulation layer69 covers the side surfaces of the light emitting cells 56,short-circuiting of the light emitting cells 56 due to a remainingmetallic material after patterning of metal layer may be prevented.

A protecting insulation layer 73 is formed on the substrate 51 with thewires 71 formed thereon. The protecting insulation layer 73 is formed ofa light-transmitting material, for example, silicon oxide layer usingchemical vapor deposition technique. In this way, a light emitting diodefor AC operation.

According to the eighth embodiment, a reliable light emitting diode forAC operation can be provided by preventing disconnection or shortcircuit of wires by external pressure, and short circuit of a lightemitting cell by a conductive material such as metal residue while thewires are formed may be prevented. Further, the wires may be formed tobe supported by insulation layers, so that a reliable light emittingdiode for AC operation can be manufactured.

Although the present invention has been described in detail inconnection with the specific embodiments, it will be readily understoodby those skilled in the art that various modifications and changes canbe made thereto within the technical spirit and scope of the presentinvention. It is also apparent that the modifications and changes fallwithin the scope of the present invention defined by the appendedclaims.

What is claimed is:
 1. A light emitting device, comprising: a substrate;a first light emitting cell disposed on the substrate and a second lightemitting cell disposed on the substrate, wherein the first and secondlight emitting cells comprise: a first semiconductor layer and a secondsemiconductor layer; an active layer disposed between the first and thesecond semiconductors layers; and a first inclined surface; a firstconductive material disposed on the second semiconductor layer of thesecond light emitting cell; a first insulation layer that overlaps thefirst conductive material and the first and second light emitting cells;a second conductive material that overlaps the first insulation layerand electrically connects the first light emitting cell and the secondlight emitting cell; and a second insulation layer that overlaps thesecond conductive material, wherein both the first insulation layer andthe second insulation layer comprise a light transmitting material; andwherein the first inclined surface is continuous and has a slope ofapproximately 20° to approximately 80° from a horizontal plane of thesubstrate.
 2. The light emitting device of claim 1, wherein the firstconductive material comprises a transparent electrode disposed on thesecond semiconductor layer of the second light emitting cell.
 3. Thelight emitting device of claim 2, wherein the first insulation layercomprises a first via hole exposing the transparent electrode.
 4. Thelight emitting device of claim 3, wherein: the first insulation layer isdisposed directly on the first semiconductor layers of the first andsecond light emitting cells; and the first insulation layer comprises asecond via hole exposing the first semiconductor layer of the firstlight emitting cell.
 5. The light emitting device of claim 4, whereinthe second conductive material comprises: an electrode pad disposed onthe first semiconductor layer of the first light emitting cell throughthe second via hole; and a wire connecting the first semiconductor layerof the first light emitting cell to the transparent electrode throughthe first via hole.
 6. The light emitting device of claim 2, wherein thetransparent electrode comprise at least one of indium tin oxide (ITO),nickel (Ni), or Gold (Au).
 7. The light emitting device of claim 1,wherein: the first inclined surface comprises the second semiconductorlayer and the active layer, the first and second light emitting cellsfurther comprise a second inclined surface comprising the secondsemiconductor layer and the active layer; and the second inclinedsurface has a slope of approximately 20° to approximately 80° from thehorizontal plane of the substrate.